In the commercial software world, user interfaces are generally designed by one group. Like Microsoft for Windows or Apple for Mac OS. Those desktop environments were designed by one company who did things like user testing and statistical analysis to try and make the desktop they thought would work best. Linux is different. Large groups definitely DO perform user testing and statistical analysis, but one group can also say "Here's what we want" and, if they have the ability to code it, their idea comes into being. It's pretty amazing, when you think about it. Linux lets people create what they want. If you don't like what's out there, fork it! Or start from scratch! You're in control!

Exactly. The opposite is true too: just because you can do it under Windows doesn't mean that you want to do it under Linux.

Linux gives you the choice of running anything from a console to the glitzy KDE environment demoed in the video. X itself will rarely be a deciding factor. Indeed, the DE may not even factor since non-technical users may simply choose a distro and leave it at that. (Granted, non-technical Linux users are rare. But they do exist!)